The invention relates to space frame structures. The invention is concerned in particular with a space frame structure of the kind described in our published United Kingdom Patent Application GB-A-2228503 (corresponding U.S. Pat. No. 5,079,890). The known space frame structure comprises an upper grid of structural members, a lower grid of structural members, interconnecting members extending between the upper grid and the lower grid and joining the grids together to form a space frame, and a concrete layer carried by the upper grid, wherein the structural members of the upper grid are at least partially embedded in the concrete to unite them structurally with the concrete and thus form a composite upper layer. The upper structural members normally have lower flanges intended to support shuttering on which the concrete layer is to be poured. Typically the structural members are I-section members so that they also have upper flanges to facilitate keying to the concrete.
The provision of both upper and lower flanges creates a problem because it then becomes difficult or impossible to insert closely fitting shuttering between the upper and lower flanges after the structure has been built. Typical shuttering is corrugated steel sheet and it is particularly desirable to have a close fit at the ends of the corrugations to prevent undue escape of poured concrete.
A further difficulty with shuttering which only partially overlaps the lower flanges is that before it becomes fixed there is a risk of it dropping through the space between the corresponding lower flanges. GB-A-2228503 also acknowledges that the upper members may be of inverted T-section and this facilitates installation of closely fitting shuttering. However the absence of an upper flange on an inverted T-section has the disadvantage of diminishing the keying between the partly embedded member and the concrete. A known compromise is to provide an irregular section with a smaller upper flange than lower flange but sections of this nature find very little use in industry and thus are not readily available. Production of such non-standard sections is expensive. Even the smaller upper flange can cause difficulties in installing a closely fitting sheet of shuttering.
An object of the invention is to overcome or to reduce the above mentioned disadvantages.